Abstract:

In order to clarify the resistance of Echinochloa crus-galli to butachlor in rice fields in Guangdong and screen alternative herbicides, the susceptibilities and resistance levels to butachlor of different Echinochloa crus-galli populations were determined by whole-plant experiment, and then the susceptibilities to 7 other herbicides were also determined. The results showed that there were significant differences in the control efficacy among different populations when treated with the recommended dosage of butachlor (active ingredient 1080 g/hm²) in pre-emergence applications; the plant control efficacies were 100% for 7 populations and were 82.7%-93.3% for 10 populations; however, the control efficacies were only 75.9%, 70.0% and 40.0% for the 21-SX-3, 21-LZ-4 and 21-LZ-7 population, respectively. When butachlor was applied pre-emergence, the resistance indices of the 21-SX-3, 21-LZ-4 and 21-LZ-7 populations ranged between 2.1 to 6.3; when butachlor was applied at the early stage of the seedlings, the resistance indices ranged between 2.9 to 6.0. In the experiments of screening alternative herbicides, the dry weight inhibition rate of pretilachlor on 21-LZ-7 population was significantly lower than that on the susceptible population 21-LZ-1, while the dry weight inhibition rates of thiobencarb, pyriminobac-methyl, pyraclonil and oxaziclomefone on both 21-LZ-1 and 21-LZ-7 population were above 90%, making them suitable as alternative herbicides for controlling butachlor-resistant E. crus-galli. In conclusion, this study indicates that some E. crus-galli populations in Guangdong have developed low to moderate levels of resistance to butachlor, and herbicides such as pyraclonil are suitable for the control of butachlor-resistant E. crus-galli populations.

Key words: Echinochloa crus-galli, butachlor resistance, resistance index, alternative herbicide